BEIJING, China (CNN) -- China has leveled new allegations in the arrest of employees of one of the world's largest mining companies, saying Rio Tinto overcharged Chinese steel mills by $100 billion over six years.

Rio Tinto signage scrolls past the opening bell at the Australian Stock Exchange in Sydney on June 5.

The latest allegations, involving the sale of iron ore, appeared on a Web site affiliated with China's state secrets administration.

A spokeswoman for Rio Tinto said Monday that the company had heard about the new accusations but did not wish to comment on it.

Last month, China arrested four company employees on suspicion of stealing state secrets.

China said the four employees bribed executives from 16 of China's major steel mills to obtain industry information.

Rio Tinto has called the allegations surprising and said it was not aware of any evidence to support an investigation.